Localization of objects requires that spatial information are the same regardless of the type of sensory input. For example, if a pedestrian approaches an intersection and a car honks, the pedestrian must identify the source of the sound cue in space and link it accurately to a corresponding visual cue in order to avoid confusion (there may be many cars) if not disaster (he may be in danger of collision). Thus the two sensory inputs must be in concordance. In the process of orienting toward the car, an eye and head movement are generated, thereby providing additional sensory cues from proprioceptive (neck) and vestibular (head) origin. These must be accurately registered internally so that the brain's depiction of the car in space remains correct. Having realized that the light had not changed, the pedestrian might then reorient toward the crosswalk button and guide his hand to press this new target. Though simple in concept, this set of behaviors requires that the brain integrate auditory, visual, proprioceptive, and vestibular inputs accurately and synchronously. All inputs must be spatially concordant; that is, the sense of a particular target location must be the same for the auditory and visual inputs. These must be integrated with internal signals conveying where the eyes are in the head, where the head is in space, where the head is on the body (neck position), and where the body is relative to the ground. Errors in these various components (sensory or motor) will result in inaccurate localization of external targets, and therefore erroneous behavior. New methods, such as "virtual reality" technology, will be used to control and shape the visual and auditory world, while new motion control devices will allow manipulation of vestibular and somatic variables. A visual display panel within arm's reach, a virtual auditory stimulus capability, and a head and finger tracking device will be added to our sled/rotator laboratory. The sled/rotator permits precise control of subject motion in space (vestibular stimuli). The addition of virtual auditory stimuli allows us to coordinate and manipulate vestibular and auditory spatial cues smoothly and independently. Visual target presentation capabilities will allow us to also independently manipulate spatial visual targets in space. These combined features will provide true multisensory stimulus capabilities across three sensory modalities, with which we can assess each influence in isolation or in combination. This past year, we have set up a development lab (light tight and near anechoic) in order to instrument and test auditory and visual stimulus methods and tasking procedures. We have begun to assess virtual auditory techniques in direct comparison with real stimuli. We are also testing auditory-visual concordance paradigms and reaching tasks before porting the system to the sled-rotator lab.